Removal of volatile products from photographic emulsions



' Patented July 21, 1953 REMovAL or VOLATILE PRODUCTS FROM .jPHO TOGRAPHIC EMULSIONS George D. Hill andaRudolp h E.. Ilamschroder, -Rochester, N. Y., assignors to Eastman'Kodak Company, Rochester, N. Y a' corporation of New ersey t No Drawing.

Application December 31, 1948, 7 Serial No. 68,744

5 I 3 Claims. (01. 95-7) This invention relates tomethods of preparing photographic silver halide emulsions andmore particularly to a processofiorming photographic emulsions wherein-by products are removed, for

example, by means of vacuum.

It is well known in the art of photographic emulsion making that it is desirable to remove soluble salts resulting from the emulsion-making reactions, especially in thosecases where the emulsion is designed for coating on transparent supports. Equally well known are emulsions of the type where ammonia is used in making the emulsion and is present in the reaction mixture after formation of, the silver halide. In such processes theammonia and any solublesalt present are customarily removed by shredding the emulsion andwashing out-.the ammonia with water. V 1

I In such processes it is customary in the art, after precipitation ofsilverhalide inthe pres-. ence of a protective colloid, to chill the emul sion so that it can be cutupand shredded, following which the pieces are'washedfor the desired time to removesalts' ordissolved material such-as-ammonia; Frequently this process requires many'hours to effect the. removal ofsalt, and ise-performed in batches in crooks, tanks,

shredding machines and; other equipment for chilling; shreddingand washing the emulsion.

It is, therefore, one object ofourinvention to provide a new methodof making ci -photographic emulsion. Another object is to provide novel methods of making and purifying a photographic emulsion. A still'further object is toprovide an economical continuous process of forming a photographic emulsion of optimum quality. Fur-1 ther objects of our invention will become apparent from consideration of the iollowin'g description.- ivv Ourinvention resides in, and the objects of our invention are accomplished 'by, reacting an aqueous ammonia solution of a silver salt, such as silver nitrate, withawater-soluble halide and removing the nitrogenous product, such as am I monia; from the reaction mixture by means of vaporization, such asby vacuum.

[- Itwill be apparent; thattwhen we use vacuum for removal of a volatile materialdissolved in. a

reaction mixture, avery economical process is made available. We have found that when vac-' uum is employed to remove ammonia or other volatile compounds from" the emulsions of our invention, ajdecided saving-intime,'materials and manpower is efi?ected. Also the photographic qualityobtainable from the emulsion so treated so 7 r methyl or trimethyl ammomum hal1des,ethyl ammonium bromide or chloride and quaternary We can use one or more of is comparable to that obtainable by the washing technique of the prior art. The quality of the product can'be higher,- especially sincethere no possibilityof emulsion contamination by impurities of the Wash water usually usedand because better control means are made available. A further advantage is the fact that the process may be continuous in operation. The above advantages will become more apparent by consideration of the following detailed description-of our invention.

The emulsions which are adaptableto use in our invention are formed by reacting a silver salt ,such as silver nitrate dissolved in an excess of ammonia or lower aliphatic amine solution, with a water-soluble halide salt such as an alkali 'metal -halide,-ammonium halide, or alkyl-substituted ammonium halide of the following structure:

where Xis a halogen atom and R, R1, R2 andRs each represents a hydrogen .atom or' an alkyl group having from one to four carbon atoms, and in which the sum of the carbon atoms is not over four; Thus, water-soluble halides which we can usefare the common ammoniumhalides, for example, ammonium chloride, bromide, or iodide and methyl ammonium bromide or chloride, di-

ammonium halides. such halides or other water-soluble metal halides, together and particularly in conjunction with an iodide such as sodium or ammonium iodide. j Gen-'- erall'y the'total number of carbon atoms in the alkyl group or alkyl groups'attached to the nitrogen atom in the above formula is less than five because the aminesof morecarbon atoms resulting from the emulsionre'action are not sufficiently'volatile to be removed by vacuum. Accordingly, we prefer. to use hydrogen halides, alkali .rhetal, ammonium or methyl ammonium halides in our invention.

Thefollowing' examples are given as illustrative of our; inventioni 1 sampl 1 7' One kg. of silver nitrate dissolved ina 10%. excess of'ammonia and made up with water to a total volume of 10 liters was added to asolution containingl kg. of gelatin and 700 grams of pota'ssium'bromidein 10.5 liters of solution. The resulting mixturewas' passedthrougha vacesters of polyvinyl alcohol and ripening or digesting operations customary in the artmay now be carried out.

Example 2 i The following solutions were prepared in, the;

usual manner:

Gelatin (16.8% aqueous) grams 6080 Potassium bromide do 665 Potassium iodide .do 10.3 Water cc 9530 Silver nitrate 1 grams 1000 Monomethylamine (25% aqueous) cc 3320 Water Solutions 1: and II were mixed as rapidly as possible at a temperature of 120 F. After a short interval at 117 F., the emulsion was passed through an outgassing apparatus and monomethylamine was partially removed until the pI-I was 10.35. The resulting emulsion was treated, ripened or digested and coated on a paper suppor't'at pH 9.15 in the manner well known in the photographic emulsion-making art exclusive of washing.

In preparing the emulsions such as above described, it is not necessary to use gelatin as the peptizing material, but other peptizing hydrophilic colloids may be used such as polyacrylam ide or imide resins as disclosed in theljoweet a1. U. S. patent application Serial No. 685,375, filed July 22, 1946 nOW U. S. Patent No. 2,541,474 granted February 13, 1951, particularly thev polyacrylamides containing to per cent combined acrylimide and imidized polyacrylamides containing to per cent combined acrylimide and 4 to 12 per cent combined acrylic acidjdescribed therein; modified proteins e. g. deriva, tives of casein, soybean protein, blood albumin, egg albumin, etc., obtained by reaction of these proteins with sufonyl chlorides, carboxylic acid chlorides, anhydrides, etc., prior or subsequent to oxidative hydrolysis with, for example, peroxide as disclosed in Lowe et al. U. S. patent appli'cation' Serial No. '7 68,480, filed August 13, 1947, and similar materials.

In a manner similar to that described "in the above examples, we can use a solution of another silver salt such as 7 silver carbonate, citrate, tartrate, acetate, sulfate, etc., and cause it to react with an alkali metal or ammonium halide and the nitrogenous by-products resulting are removed as by evacuation of the reaction mixture, washing not being-employed. Therefore, according to our invention, when an aqueous ammoniasolution of a silver salt is reacted with one of the halides, the resulting reaction mixture contains silver halide, volatile nitrogenous products as ammonia or an amine, and a water-soluble, nonsalt.

Inorder to remove ammonia from the emulsion systems described, we have found it advisable to supply heat to the liquid being evacuated to compensatefor the drop in temperature arising from the heat supplied for vaporization and the tendency for the rate of removal of ammonia to fall with drop in temperature thereby. The rate and extent of the removal of moist ammonia is, of course, controlled on the one hand by the peculiaritiesof the vacuum equipment and the flow of the liquid through it, which naturally d'e' pends somewhat on the capacity of the vacuumpumping means. We have found that the most useful range of operation includes a range of pressure in the vacuum system of from 20 to 30 mm. of mercury, and when heat is supplied to the liquid film by means of a water jacket, a range of temperature from 60 to C. in the jacket is mostsatisfactory. However, in a typical all-glass installation using water jackets and aspirator pumps, appreciable amounts of ammonia are quickly removed with the water temperature at 40 C. and a vacuum pressure of mm. As is apparent, the most suitable or desirable conditions of rate of flow-temperature and pressure for a given apparatus are readily determinable but depend on definite characteristics of that equipment. After we determine the characteristics ofthe vacuum system, that is, its rate of removal of ammonia, or volatile dissolved product, we are next governed by'matters of economy and photographic quality. That is, in certain instances where it is desired to remove'substantially all of the ammonia from the reaction mix ture, we can do so by selection of the optimum conditions of temperature, pressure and rate of flow through the evacuation chamber; In other cases where we have use for an emulsion from which all of the ammonia has not been removed, we naturally increase the rate of flow or lower temperature or increase the pressure, or we can vary one or more of these conditions at the same time, as will be apparent to those skilled in the art.'

Since the grain characteristics and photo.- graphic properties of-an ammoniacal emulsion are controlled by the concentration, temperature and time of the ammonia solutions in contact with-the silver'salt, it is desirable to operate our invention in such a 'Way that the grains of silver salt are ripened and the ammonia is reduced in concentration to less than 22 grams per kilogram of silver nitrate converted to silver halide in a total time of less than 2 hours. This we may accomplish either by-short ripening and slow removal or by more prolonged ripening and fast removal or short ripening and fast removal.

One advantage and unique feature of our process is now apparent. Having determined the'opcrating characteristics of the emulsion-making system, we may remove practically any quantity of ammonia or volatile material from the silver halide reaction mixture. If we-desire an'emuli n h v n 119? t e characteristics derivable from ,a similar well-washed emulsion, we removetha't amount of ammonia'which corresponds to washing, and it is not ne'cessar'yito remove dissolved salts to obtain this'quality. Similarly, if desired, we remove less ammonia with the result, among otherth i'ng's, of obtaining an appreciable increase" in the output of the evacuation system.

Since sensitometriccharacteristics and photographiequality areof prime importanca'we rec move an amount of ammonia commensurate' with sions are coated on supports such as paper.

Thus there is made available a process whereby we can remove practically all or part of the ammonia' associated with the silver halide then, if desired, we can add ammonia in definite quantities during finishing operations, but We are not limited, as by washing methods, to the grain characteristics obtained while the silver halide is in contact with ammonia during a washing period.

Finished emulsions having desirable photographic qualities can be made byremoving ammonia until a range of from about to 22 grams,

of ammonia per kilogram of silver nitrate used in making the emulsion and converted to'silver halide, remains associated with the silver halide. That is, the volatile nitrogen compounds present in the reaction mixture. are removed until the molecular equivalent amount of the nitrogen compound remaining in the emulsion is equal to less than about 22 grams of ammonia per kilogram of silver nitrateused.

It will be apparent that when an alkyl-substituted' ammonium halide is used, the efliciency of our process may be lowered principally because of the higher boiling pointof the aliphatic amine .formed in the reaction and which is to be removed from the reaction mixture. In such cases we may desire to wash the material from the emulsion with or without previous evacuation treatment as we can do when water-soluble halides or ammonium or alkali metal halides are used. Similar1y, when the nitrogenous product such as ammonia is highly volatile, we'may partially or completely dispense with vacuum treatment and remove the ammonia by passing a strong current of air over the surface of the reaction mixture, by means of efiicient liquid film vapor exchangers.

In certain cases it may be desirable to carry out the evacuation of the emulsion before or. after ripening or digesting or other steps known to emulsion making. However, we prefer to remove a material such as ammonia prior to ripening of the emulsion. Our process is especially adaptable to removing the ammonia just after or as soon after formation of silver halide as it possible and, therefore, may readily be adapted to a continuous manufacturing process. We merely precipitate the halide a'sdescribed, then conduct the silver halide reaction mixture in a continuous manner from the reaction chamber to the evacuation chamber, and if the evacuation system 1 is operated at a fairly low capacity, weuse atem- 7 halide grain size is capable of beingcontrolled cording to our-invention.

It-is to be understood that thedisclosure herein is by way of example, and that we consider as included in our invention all modifications and more readily then previously operating acequivalents falling within thescope of thesappended claims.

What we claim is:

'1. The method of making a photographic silver halide emulsion which comprises reacting in an excess of aqueous ammoniacal solution in the presence of a peptizing hydrophilic colloid for silver halide, substantially equivalent quantities ofssilver nitrate and a water-soluble halide salt selected from the group'consisting of alkali metal halides, ammonium halides and methylamine halides, to yield silver halide, a, volatile nitrogenous product and a water-soluble non-volatile salt product, removing said volatile nitrogenous product from said emulsion only by passing the emulsion as a thin film of liquid through a chamber maintained at a pressure of from about 20-90 mm. of mercury and a temperature of from about -80 C; until the molecular equivalent amount of the nitrogenous product remaining in the emulsion is equal to less than about 22 grams of ammonia per kilogram of silver nitrate originally used in making the emulsion and converted to silver halide, and digesting the emulsion, the removal of nitrogenous product and digestion being effected within less than two hours.

2. The method of making a photographic silver halide emulsion which comprises reacting in an excess of aqueous ammoniacal solution in the presence of a peptizing hydrophilic colloid for silver halide, substantially equivalent quantities of silver nitrate with an alkali metal halide, to yield silver halide, a volatile nitrogenous product and alkali metal nitrate product, removing said volatile nitrogenous product from said emulsion only by passing the emulsion as a thin film of liquid through a chamber maintained'at a pressure of from about 30-90 mm. of mercury and a temperature of from about ell- C. until the molecular equivalent amount of the nitrogenous product remaining in the emulsion is equal to less than about 22 grams of ammonia per kilogram of silver nitrates originally used in making the emulsion and converted to silver halide, and digesting the emulsion, the removal of nitrogenous product and digestion being effected within less than two hours.

3. The method of making a photographic silver 7 7 per kilogram of silver nitrate originally used in making the emulsion and converted to silver halida'and digesting the emulsion, the removal of ammonia and digestion being efiected within less than two years.

GEORGE D, HILL. RUDOLPH E. DAMSCI-IRODER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,861,918 Hickman -2 July 7,1932 2,158,219 Claus May 16, 1939 2,256,356 Russell et a1. Sept. 16, 1941 15 8 FOREIGN PATENTS Number Country Date 3,782 Great Britain 1873 477,315 Great Britain Mar. 23, 1936 OTHER. REFERENCES Wall: Photographic Emulsions, published by American Photographic Publishing 00., 1929, pp. 221, 222, 223, 225 and 226, cited. j

The Amateur Photographer, volume 18, pp. 223, 224, 242 and 243.

The British Journal of Photography (1883), pages 41, 42 and '71. 

1. THE METHOD OF MAKING A PHOTOGRAPHIC SILVER HALIDE EMULSION WHICH COMPRISES REACTING IN AN EXCESS OF AQUEOUS AMMONIACAL SOLUTION IN THE PRESENCE OF A PEPTIZING HYDROPHILIC COLLOID FOR SILVER HALIDE, SUBSTANTIALLY EQUIVALENT QUANTITIES OF SILVER NITRATE AND A WATER-SOLUBLE HALIDE SALT SELECTED FROM THE GROUP CONSISTING OF ALKALI METAL HALIDES, AMMONIUM HALIDES AND METHYLAMINE HALIDES, TO YIELD SILVER HALIDE, A VOLATILE NITROGEN NOUS PRODUCT AND A WATER-SOLUBLE NON-VOLATILE, SALT PRODUCT, REMOVING SAID VOLATILE NITROGENOUS PRODUCT FROM SAID EMULSION ONLY BY PASSING THE EMULSION AS A THIN FILM OF LIQUID THROUGH A CHAMBER MAINTAINED AT A PRESSURE OF FROM ABOUT 20-90 MM. OF MERCURY AND A TEMPERATURE F FROM ABOUT 40-80* C. UNTIL THE MOLECULAR EQUIVALENT AMOUNT OF THE NITROGENOUS PRODUCT REMAINING IN THE EMULSION IS EQUAL TO LESS THAN ABOUT 22 GRAMS OF AMMONIA PER KILOGRAM OF SILVER NITRATE ORIGINALLY USED IN MAKING THE EMULSION AND CONVERTED TO SILVER HALIDE, AND DISGESTING THE EMULSION, THE REMOVAL OF NITROGENOUS PRODUCT AND DIGESTION BEING EFFECTED WITHIN LESS THAN TWO HOURS. 